In a large saucepan, melt the butter over low heat. Once melted, add the mini marshmallows and stir continuously until completely melted and smooth.
Remove the saucepan from heat and stir in the salted caramel sauce and vanilla extract until well combined.
Gradually add the Rice Krispies cereal to the marshmallow mixture, stirring until all the cereal is evenly coated.
Lightly grease a 9x13-inch baking dish with cooking spray or butter. Pour the mixture into the dish and press it down firmly with a spatula or your hands to create an even layer.
Sprinkle the sea salt over the top of the pressed mixture. Allow the treats to cool at room temperature for about 30 minutes.
Once cooled, cut into squares or rectangles and drizzle with extra salted caramel sauce if desired.